Polyfunctional (per)fluoropolyethers are well known in the art to be useful intermediates for the manufacture of low Tg polyfunctional (per)fluoropolyether derivatives or cross-linkable macromers.
Thus, U.S. Pat. No. 5,719,259 (E. I. DU PONT DE NEMOURS AND COMPANY) 17 Feb. 1998 discloses anionic copolymerization of hexafluoropropylene oxide with a perfluoroalkylene oxide like, notably, perfluoroallylfluorosulfate oxide, in the presence of an initiator, namely a complex of a cesium perfluoroalkoxide of a hexafluoropropylene oxide oligomer and a poly(ethylene glycol)dimethyl ether, to yield polyfunctional perfluoropolyethers comprising recurring units having the following general formula: —(CF(Rf)CF2O)m(CF(COF)CF2O)n, wherein Rf is a C1-C8 perfluoroalkyl group and the m:n mole ratio ranges from 2:1 to 50:1.
The —CF2OSO2F side-chain functional groups derived from perfluoroallylfluorosulfate oxide monomer undergo in situ nucleophilic replacement in the presence of said initiator with cleavage of the S—O bond to afford —COF functional groups, so that final polymer is exempt from such fluorosulfate groups, but rather comprises acyl fluoride moieties.
The polyfunctional perfluoropolyethers so obtained typically have a Tg of from about −45° C. to −70° C.
Also, EP 1074584 B (SOLVAY SOLEXIS S.P.A.) 22 Jun. 2005 discloses perfluoropolyethers comprising —O(CF2)2SO2F side-chain functional groups, said perfluoropolyethers being homopolymers of CF2═CFO(CF2)2SO2F or copolymers of said monomer with perfluoroolefins like, notably, tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). It is well known that fluorosulfonic —O(CF2)2SO2F functional groups have a reactivity totally different from groups comprising fluorosulfate moieties. These groups are typically converted into —O(CF2)2SO3H groups, but cannot be easily converted in other functional moieties (e.g. amides, carboxylic esters, etc.).
Attempts were also made in the past for incorporating reactive moieties other than fluorosulfonic groups in main chain of (per)fluoropolyether derivatives by oxidative photopolymerization of ethylenically unsaturated perfluoromonomers with functional fluoroalkylenes.
EP 1568725 B (SOLVAY SOLEXIS S.P.A.) 18 Jun. 2008 discloses peroxidic perfluoropolyethers prepared by photooxidation of TFE with perfluoroethylene sulphonyl fluoride, CF2═CFSO2F, said perfluoropolyethers comprising two functional end groups independently selected among —CF2COF, —COF and —SO2F. EP 1568730 A (SOLVAY SOLEXIS S.P.A.) 31 Aug. 2005 discloses peroxidic perfluoropolyethers prepared by photooxidation of TFE with perfluoroacryloyl fluoride, CF2═CFCOF, said perfluoropolyethers comprising two functional end groups independently selected between —CF2COF and —COF.
However, no incorporation of the CF2═CFSO2F and CF2═CFCOF functional fluoroalkylene monomers into the perfluoropolyether main chain occurred during the radical photo-oxidative polymerization of said monomers with TFE: these monomers were thus found to only behave as chain transfer agents by cleavage of the functional group.
The need was thus felt to provide (per)fluoropolyethers comprising chain recurring units comprising at least one —CF2OSO2F side-chain functional group to be easily derivatized into a wide range of functional (per)fluoropolyether derivatives, thanks to the versatility and reactivity of fluorosulfate group.